In a power IC, a power device is controlled and examined by low-voltage integrated circuits. The voltage of the power supply for a low-voltage integrated circuit should be much lower than the voltage of the power supply for a power device. Although a low-voltage power supply can be realized by a switch formed by high-voltage devices, which can convert high-voltage power supply to low-voltage power supply through a converter, at least one low-voltage power supply is necessary for the initial switching operation. The low-voltage power supply can be a charged capacitor and it can be charged by connecting it to a high-voltage terminal through a resistor. [1] In order to reduce the cost, an active resistor is always used, which must be a normally-on device (for example, a depletion mode high-voltage MOST). And the “off” state of the normally-on device is realized when the capacitor is charged up to a certain voltage.[2] However, power devices are mostly normally-off devices. A higher fabrication cost may be incurred due to that both normally-off and normally-on high-voltage devices have to be implemented in one chip.